The present invention relates to a method and an apparatus for boring openings in a cylindrical block and, more particularly, a method and apparatus for boring riser holes through a cylindrical graphite block.
The preferred method for manufacturing cast steel railroad wheels is the bottom pressure casting foundry operation wherein molten steel under pressure is forced upwardly into a graphite mold to fill the mold from the bottom upwardly. This bottom pressure casting operation eliminates many of the concerns associated with the traditional top pouring of molten steel in foundry operations such as splashing and insufficient filling of molds. Further, the use of machined graphite molds assures dimensional accuracy. In the casting of railroad wheels, it is usual for the outer side of the wheel, which also corresponds with the top half of the mold or the cope, to include a raised center hub portion and, depending on the size of the wheel, from 6 to 14 raised riser sections extending from the plate portion of the wheel near the rim.
Referring to FIGS. 1-6, the graphite mold itself comprises a top half or cope 10 and a bottom half or drag 12. Both cope 10 and drag 12 are large cylindrical blocks of graphite designed to withstand the 3,000xc2x0 F. temperature of molten steel used to manufacture the railroad wheel 18. It should be understood that each of the cope 10 and drag 12 are in the neighborhood of from 28 to 52 inches in diameter, corresponding to the size of railroad wheel being manufactured and, upon initial use, about 18 inches in height.
Cope 10 is seen to have the outer section of railroad wheel 18 machined therein, along with risers 16 extending upwardly from the cavity for railroad wheel 18 as well as hub opening 14. Drag section 12 is seen to include an ingate 20 which is adapted to receive a pouring tube and thus the molten metal to be upwardly poured under pressure from the reservoir in the pouring ladle below.
Upon the pressure pouring of the molten steel upwardly through ingate 20, wheel cavity 18 is filled with molten steel which extends upwardly into riser openings 16 and hub opening 14 a predetermined distance. Such additional metal in hub opening 14 and riser openings 16 is necessary such that additional molten metal is available to pour downwardly into the railroad wheel 18 mold during cooling and solidification of the wheel just after pouring.
The various prior art steps in preparing the cope section 10 of the graphite mold will now be described. Referring to FIG. 2, the cope section 10 is seen to comprise a cylindrical block of graphite with dimensions as described above. Such cope 10 is placed in a vertical boring mill wherein boring mill bit 22 is centered to bore hub opening 14 into cope section 10.
Next, template 26 usually made of aluminum of a thickness of about xe2x85x9cth of an inch as shown in FIG. 3 is placed on top of cope 10. Such template 26 is premachined for a series of riser openings at various radial distances from the center. The inner most diameter riser locator openings at 32; the mid diameter riser locator openings at 30 and the outermost diameter riser locator openings at 28. Such riser openings are premachined in template 26 to correspond with the desired location of risers in the various size copes 10 as required in the manufacture of varying diameter railroad wheels. It is seen that center opening 34 in template 26 is designed to be positioned above hub opening 14 in cope 10.
Referring to FIG. 4, each of riser locator openings 28, 30 and 32 have a raised section 36 extending upwardly such that an associated hand drill bit 40 can be manually centered within the riser locator openings 28, 30 and 32. An initial locating opening 42 is drilled into cope 10 for ultimate location of each riser opening 16. Referring to FIG. 5, such drilled locator openings 42 are shown in cope 10.
As seen in FIGS. 5 and 6, cope 10 is seen positioned on drill press table 47. Trepanning tool 44 includes a projecting locating pin 45 extending from the end thereof. Locating pin 45 is adapted to be placed within riser locating openings 42 in order that risers 16 can be cut at the exact location established by the use of template 26 with the predrilling of locator openings 42.
Another problem with the existing method of drilling riser openings in the graphite block is for the openings farthest from the drill press support, it is difficult to achieve the desired perpendicular alignment of the openings due to loose fit tolerances with the moving parts of the radial drill press. This problem is magnified when the distance the drill press spindle must travel from the support column is greatest.
Accordingly, it is an object of the present invention to provide an improved method and apparatus for drilling openings in a material block.
It is also an object of the present invention to provide an improved method and apparatus for drilling riser openings in a cylindrical graphite block to be used in the casting of steel railroad wheels.
An improved method and apparatus of drilling riser openings in a graphite block is provided by the present invention. It has been established that from an efficiency and accuracy point of view, it is best to keep the drill press spindle as close to the drill press support along the drill press arm as possible. Accordingly, it was established that since the cope graphite mold has the riser openings at a single radial distance from the center of the cope, it would be possible to rotate the graphite block to the preselected locations and, without the drill press spindle moving, drill the desired riser openings in the graphite block.
An indexing plate is provided that is circular in shape and is mounted to the drill press table in a manner that allows the index plate to rotate about a central axis. The graphite block is placed in the index plate in a manner such that rotation of the index plate is accompanied by rotation of the graphite block. It such be understood that the graphite block is extremely heavy, weighing about 1,000 pounds when at its initial thickness of 18 inches; so that rotation of the supporting index plate is accompanied by rotation of the graphite block placed therein.
An indexing plate support is provided in such that rotation of the indexing plate can be controlled to very accurate increments. Such increments are possible due to predrilling and aligning openings in the indexing support and the indexing plate to allow a pin or pins to position the indexing plate with relation to the indexing plate support. Alternatively, a movement mechanism can be associated with the indexing plate support such as gearing or other motorized control to allow the accurate rotation of the indexing plate through the indexing plate support to preselected locations.
Utilizing such rotation of the indexing plate and the graphite block placed therein, it is possible to locate the drill press spindle at a single location on the drill press arm that is as close as possible to the drill press support for the particular design graphite block and desired location of the riser openings. The indexing plate support is utilized to allow the positioning of the indexing plate and graphite block at the desired location such that the drill head, drill press spindle and drill operate to drill the first riser opening in the graphite block. This is done without the need for the template or initial locator openings mentioned as part of the prior art system.
When the first riser opening is drilled, the indexing plate support is utilized such that the indexing plate is rotated bringing the next desired riser opening location in line with the drill press spindle and drill without moving the drill press spindle or the drill press arm. Further, the drill press spindle remains at the desired location as close as possible to the drill press support. The next riser opening is drilled in the graphite block at the exact same radial distance from the center point of the graphite block. This assures the accurate and perpendicular drilling of the risers and the graphite block since the drill press spindle is at a location as near as possible to the drill press support thereby minimizing its extension outwardly along the drill press arm. Such location of the drill press spindle at the minimum distance from the drill press support along the drill press arm decreases the potential for non-perpendicular drilling of the riser openings.